Apparatus and method for intravascular catheter navigation using the electrical conduction system of the heart and control electrodes

ABSTRACT

A new apparatus, algorithm, and method are introduced herein to support navigation and placement of an intravascular catheter using the electrical conduction system of the heart (ECSH) and control electrodes placed on the patient&#39;s skin.

PRIORITY

This application is a continuation of U.S. patent application Ser. No.15/850,664, filed Dec. 21, 2017, now U.S. Pat. No. 10,321,846, which isa continuation of U.S. patent application Ser. No. 14/678,986, filedApr. 5, 2015, now U.S. Pat. No. 9,854,992, which claims priority to U.S.Provisional Application No. 61/977,120, filed Apr. 9, 2014, each ofwhich is incorporated by reference in its entirety into thisapplication.

FIELD OF THE INVENTION

The Invention relates to the field of intravascular catheter navigation,tracking or guidance through the vasculature and of intravascularcatheter tip location and placement. Currently, fluoroscopy can be usedfor both catheter navigation and tip location of intravascularcatheters. In the case of central venous catheters, navigation supportis currently provided by methods, such as fluoroscopy, magnetic,infrared, blood pressure or Doppler-based. ECG-based methods are usedcurrently only for catheter tip location at the cavo-atrial junction inthe proximity of the sinoatrial node. ECG-based methods are notcurrently used for catheter navigation or tip location at otherlocations in the vasculature or for catheter navigation. The purpose ofthe present Invention is to provide a single device for bothintravascular catheter navigation and tip location at differentlocations in the vasculature, in the venous as well as in the arterialsystem without using X-ray or fluoroscopy.

BACKGROUND OF THE INVENTION

In many clinical situations it is essential to know the exact locationof the tip of a catheter inserted in the body of a patient. It is alsovery helpful to be able to navigate the catheter through the patient'sbody, i.e., to follow the movements of the catheter tip, e.g., duringcatheter insertion. Currently, fluoroscopy can be used for catheternavigation and tip location of intravascular catheters. In the case ofcentral venous catheters, navigation support is currently provided bymethods, such as fluoroscopy, magnetic, or Doppler-based which have eachtheir own benefits and limitations. ECG-based methods are used currentlyonly for catheter tip location at the cavo-atrial junction in theproximity of the sinoatrial node. ECG-based methods are currently notused for catheter navigation.

There exists currently a need for an accurate, safe, intra-proceduraland easy-to-use device, which allows, in a single device, for navigationand tip location of catheters at different locations in the vasculature,in the venous as well as in the arterial systems, which works for a widerange of catheter types and clinical applications, and which does notuse radiation-based methods like X-ray and fluoroscopy.

A system and method for catheter mapping is described in U.S. Pat. No.5,983,126, which uses a catheter equipped with at least a measuringelectrode and a reference electrode on the patient to whichtriangulation signals are applied such that the a three-dimensionallocation of the catheter tip within the body can be calculated. U.S.Pat. No. 8,155,732 describes an ECG system for ECG signal measurement ofintracardiac ECG using a switch and a processor to amplify thedifference of a chest lead signal electronically connected to a catheterand a patient limb ECG signal in order to provide a catheter tiplocation signal without using any other surface ECG leads. U.S. Pat. No.8,388,541 describes an integrated catheter placement system, which usesa magnetic tip location sensor for temporary placement on the patient'schest to detect the magnetic field of a stylet disposed in the a lumenof the catheter.

SUMMARY OF THE INVENTION

A new apparatus, algorithm, and method (all called Invention) areintroduced herein to support navigation and placement of anintravascular catheter using the electrical conduction system of theheart (ECSH) and control electrodes placed on the patient's skin.According to the present Invention, an intravascular catheter can beguided both in the arterial and venous systems and positioned atdifferent desired locations in the vasculature in a number of differentclinical situations. The catheter is connected to the apparatus using,for example, sterile extension cables, such that the apparatus canmeasure the electrical activity at the tip of the catheter. Anotherelectrode of the apparatus is placed for reference on the patient'sskin. In one embodiment of the present Invention, a control electrode isplaced on the patient's chest over the manubrium of the sternum belowthe presternal notch. In this case, if a catheter is inserted in thevenous system, for example in the basilic vein, the Invention willindicate if the tip of the catheter navigates from the insertion pointin the basilic vein into the subclavian vein on the same side, into thesubclavian vein counter laterally, into the jugular vein, into thesuperior vena cava, into the cavoatrial junction (CAJ), into the rightatrium (RA), into the right ventricle (RV), or into the inferior venacava (IVC). For the same location of a control electrode, if a catheteris inserted in the arterial system, the Invention will indicate when thetip of the catheter is navigating into the arch of the aorta, into theright coronary artery, into the left circumflex artery, or into the leftventricle (LV).

In another embodiment of the present Invention, a control electrode canbe placed on the sternum over the xiphoid process. In one embodiment ofthe present invention, a catheter can be inserted in the arterialsystems by arterial radial, brachial or axillary access. In anotherembodiment of the present Invention, a catheter may be inserted intoeither the arterial or the venous systems by femoral or saphenousaccess.

In one aspect of the present Invention, navigation maps are introducedfor different locations in the vasculature which allow for easyidentification of the location of the catheter tip.

In another aspect of the present Invention, a novel algorithm isintroduced to compute a navigation signal in real time using electricalsignals from the tip of the catheter and from control electrodes.

In another aspect of the present Invention, a novel algorithm isintroduced to compute in real time navigation parameters from thenavigation signal computes according to the present Invention.

In another aspect of the present Invention, a method is introduced whichmakes use of the navigation signal to allow for placing an intravascularcatheter at a desired location in the vasculature relative to the ECSHand to the control electrodes placed on the skin.

In another aspect of the present Invention, the electrical signalsobtained from control electrodes and from the tip of the catheter may begenerated by the natural ECSH, e.g., the sino-atrial node (SAN), byartificial (implanted) pacemakers or by electrical generators externalto the body.

In yet another aspect of the Invention, an apparatus is introduced whichsupports data acquisition required by the computation of a navigationsignal according to the present Invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1: Apparatus according to the present Invention connected topatient in supine position for access to the subclavian veins, internaljugular veins (IJ), SVC, CAJ, RA, IVC, and RV by upper body venousaccess or for access to the aortic arch, left heart and coronaryarteries by arterial radial, brachial or axillary cannulation.

FIG. 2: Map of navigation signals for access to the subclavian veins,internal jugular veins (U), SVC, CAJ, RA, IVC, and RV for upper bodyvenous access according to the present Invention.

FIG. 3: Method of navigation to the CAJ based on navigation signals andnavigation parameters calculated according to the present Invention forupper body venous access.

FIG. 4: Apparatus according to the present Invention connected topatient in supine position for cannulation of the femoral or saphenousveins or of the femoral artery

FIG. 5: Map of navigation signals for access to the superior subclavianveins, internal jugular veins (U), SVC, CAJ, RA, IVC, and RV for femoralor saphenous venous access according to the present Invention

FIG. 6: Method of navigation to the CAJ based on navigation signals andnavigation parameters calculated according to the present Invention forfemoral or saphenous venous access.

FIG. 7: Flow chart and algorithm generating navigation signals andnavigation parameters according to the present Invention.

FIG. 8: Parameter computation algorithm according to the presentInvention.

DETAILED DESCRIPTION

FIG. 1 illustrates the apparatus connected to a patient (100) in supineposition for access to the subclavian veins, internal jugular veins (U),SVC, CAJ, RA, IVC, and RV by upper body venous access or for access tothe aortic arch, left heart and coronary arteries by arterial radial,brachial or axillary cannulation. A control electrode (CE) (120) ispositioned on the patient at a location of interest. This Inventionallows for tracing the tip of an intravascular catheter relative to theCE and to the electrical conduction system of the heart (ECSH) (160).

The ECSH contains the following elements:

-   -   a) the sino-atrial node (SAN), whose electrical activity can be        seen as the P wave or P segment on an ECG waveform,    -   b) the atrio-ventricular node (AVN) including the Bundle of His        (BH), whose electrical activity can be seen as the PR segment on        the ECG waveform    -   c) the Purkinje fibers (PF), whose electrical activity can be        seen as the QRS complex on the ECG waveform    -   d) The ventricle myocardium (VM), whose repolarization includes        the J wave, ST-segment, and the T- and U waves on the ECG        waveform.

The natural/primary pacemaker of the heart is the SAN. It normal sinusrhythm, the SAN generates pulses at a rate of 100 times per minute. Ifthe SAN does not function normally, the AVN and the BH will normallydischarge and produces pulses at about 40-60 beats-per-minute. If theSAN and AVN both do not function normally, the PF will also producespontaneous pulses at about 30-40 beats-per-minute. The AVN/BH and thePF can be considered secondary (ectopic) natural pacemakers. The reasonthe SAN normally controls the whole heart is that its pulses arereleased more often to the heart's muscle cells than those from AVN/BHor PF. With other words, under normal conditions, a pulse generated bythe SAN passes down the ECSH and arrives before the other pacemakershave had a chance to generate their own spontaneous pulses.Nevertheless, under abnormal conditions in unhealthy hearts, e.g.,arrhythmias, or, even in healthy hearts, in response to variousstimulating events, e.g., overstimulation, the secondary pacemakers mayalso generate their own pulses. In such situations, secondary pacemakerscan also be used for catheter navigation according to the presentinvention.

Another important aspect of the ECSH related to catheter navigation isthe location of the different natural pacemakers in the heart wallsrelative to certain blood vessels. Thus, the SAN is located close to thejunction between the SVC and the RA, i.e., at the upper end of the CAJ.Therefore, proximity to the SAN as measured using electrical signals atthe tip of the catheter (P wave or P segment) may indicate a cathetertip location in the venous system at CM. The AVN is located between theatria and the ventricles, near the atrial septum and is supplied byblood coming through a branch of the right coronary artery and of theright of left circumflex arteries. Therefore, proximity to the AVN asmeasured using electrical signals at the tip of the catheter mayindicate a catheter tip location in the arterial system in the right orcircumflex coronary arteries. Further, certain modifications of the PRsegment in the proximity of the AVN may indicate a position of the tipof the catheter in the aortic arch. Further, certain modifications ofthe QRS complex, of the ST segment and/or of the T and U waves mayindicate a position of the tip of the catheter at specific locations inthe ventricles, i.e., in the right ventricle in case of venous access orin the left ventricle in case of arterial access.

As the catheter navigates through the vasculature, the present Inventionuses electrical signals generated by the ECSH to indicate where thecatheter tip is relative to the ECSH and to the control electrodes. Inone embodiment of this Invention illustrated in FIG. 1, the CE is placedon the manubrium of the sternum right below the presternal notch. Thisskin position is estimated to be the closest position on the skincorresponding to the upper end of the superior vena cava (SVC) in thevasculature. In addition, this position is easily identifiable byanatomical landmarks and is independent of the side of the vascularaccess location (left or right). For the same targeted position of thecatheter tip in the vasculature, the CE may be placed at other locationson the skin, as well. The CE may be placed at other locations on theskin for different targeted positions of the catheter tip.

A reference electrode (RE) (110) is placed on the patient's skin. In oneembodiment of the Invention, the RE is placed on the left lower patientabdomen right below the last rib. The RE may be placed at otherlocations, as well. A catheter (130) is inserted into the vasculature ofthe patient and electrical connectivity is ensured between the distalend of the catheter (132) and its proximal end (134). Such electricalconductivity can be ensured with currently available means, e.g., byusing a conductive wire between the catheter ends or by injectiveelectrically conductive solution like saline or heparin into thecatheter. The proximal end of the catheter (134) is electricallyconnected to the apparatus (140) according to the present Invention. TheCE (120) and the RE (110) are also electrically connected to theapparatus (140). The apparatus (140) measures an electrical signal (150)at the CE relative to the RE and another electrical signal (154) at thedistal end of the catheter relative to the RE.

The apparatus, e.g., computer, computes navigation signals (152) and(162) based on the signal (154) obtained from the distal end of thecatheter and from the signal (150) obtained from the CE. In oneembodiment of the present Invention, the electrical signals obtainedfrom the CE and from the tip of the catheter are generated by the ECSH(160), e.g., by the sino-atrial node. In another embodiment of thepresent invention, the electrical signals obtained from the CE and fromthe tip of the catheter are generated by artificial (implanted)pacemakers or by electrical generators external to the body.

FIG. 2 illustrates a map of navigation signals according to the presentInvention for access to the subclavian veins, internal jugular veins(U), SVC, CAJ, RA, IVC, and RV for upper body venous access. The heart(200) and the venous system for the upper body are illustratedcontaining the following: inferior vena cava (202), superior vena cava(204), the left innominate (or brachiocephalic) vein (218), the rightinnominate (or brachiocephalic) vein (214), the left (220) and right(206) subclavian veins, the left (224) and right (208) brachial veins,the left (222) and right (210) axillary veins and the left (216), right(212) internal jugular veins, the CAJ (272), the RA (273), the RV (275),the SAN (270), the AVN/BH (271), and the PF (277). The anatomicallandmarks illustrated in FIG. 2 are left (230) and right (231) claviclesand the presternal notch (232).

If a CE (245) is placed on the patient's skin right below the presternalnotch over the manubrium of the sternum and an RE (240) is placed on thepatient's skin right below the lowest left rib on the patient's abdomenthen the illustrated navigations signals are computed and displayedaccording to the present Invention. In a brachial vein (208, 224), thenavigation signal will present large negative amplitude aligned with theR-peak of the heart cycle (250). In a subclavian vein (206, 220), thenavigation signal will present a smaller negative amplitude aligned withthe R-peak (252, 258 respectively). Entering the innominate veins (214,218) and approaching the CE (245) the navigation signal will result in asmall biphasic navigation signal (256). At this location, theintravascular catheter tip is closest to the control electrode placed onthe patient's skin. Ideally the signal at this catheter tip locationshould be zero indicating that the catheter tip is practically at thelocation with the control electrode. The real biphasic aspect of thenavigation signal when the catheter tip is closest to the CE is a resultof a difference in phase between the ECG waveform at the tip of thecatheter and at the CE. The closer the tip of the catheter is to the CE,the smaller the phase difference illustrated by (256). This phasedifference may be used according to the present Invention to determinewhen the catheter tip is closest to the CE and to analyze the trend ofthe catheter tip movements towards and away from the CE.

Advancing the catheter tip in the superior vena cava (204) will producesmall positive amplitude aligned with the R-peak (260). In the jugularveins (212, 216), the navigation signal will have smaller negativeamplitude aligned with the R-peak of the heart cycle (254), whereby thenegative amplitude in the left jugular will be slightly larger than thenegative amplitude in the right jugular due to the fact that the leftjugular is further away from the SAN of the ECSH than the right jugular.The navigation signal computed at CAJ (272) is illustrated by (262) inFIG. 2. A large positive amplitude aligned with the P-segment of theheart cycle can be seen to the left of a small positive peak alignedwith the R-peak of the heart cycle. Advancing the catheter into the RA(273) will result in the navigation signal illustrated in (264), FIG. 2with a distinctive biphasic amplitude aligned with the P-segment of theheart cycle to the left of a small positive peak aligned with theR-peak. In the RV (275), the navigation signal is illustrated in FIG. 2by (269), whereby a large amplitude aligned with the QRS complex and alarge amplitude aligned with the T-wave indicate the proximity to thecatheter tip of the AVN/BH or of the PF (277). The duration and sizes ofthe PR segment, QRS complex and of the T-wave will vary according to thespecific location of the catheter tip in the RV, i.e., closer to thetricuspid valve (closer to the AVN/BH) or closer to the bottom of the RV(closer to the PF) or potentially in contact with the RV wall.

In one embodiment of the present invention, a weighted average orweighted difference (delta) of the CE and catheter tip signals iscomputed for the navigation signal. The weighted difference has theeffect of diminishing the elements of the ECG waveform which are similarbetween the CE and the catheter tip and enhancing the elements of theECG waveform which are different between the CE and the catheter tip.The similar elements are typically those static, i.e., not related tothe catheter tip location. The different elements are typically thosewhich change with the catheter tip location. For example, the R-peak ofthe ECG waveform is diminished, as is the T-wave if they do not dependon the catheter tip location. On the contrary, if they depend on thecatheter tip location, the P-wave is enhanced and so are changes in theQRS complex or T-wave thus enhancing the ability to discriminate betweenchanges in the navigation signal which are most relevant to catheter tiplocation changes.

These illustrations are not limitations of the present Invention. Othershapes of the navigation signals can be calculated as indicative of thelocations in the vasculature. Such different shapes or variations of thenavigation signal may depend on the location of the CE and the RE, maybe a result of patient variability, of certain parameters of thecomputation algorithms, etc.

In another embodiment of the present Invention, a navigation map can bedeveloped according to the present invention for catheter locations inthe arterial system for the same placement of the CE and RE as in FIG.2. The upper body access in the arterial access situation is performedby arterial radial, brachial or axillary cannulation. The catheter isthen advanced into the aortic arch and then further into the coronaryarteries. As the catheter tip approaches the aortic arch which is closeto the CE, a biphasic navigation signal as the one illustrated in FIG. 2(256) will be calculated according to the present Invention. As, forexample, the catheter tip is advanced into the right coronary artery,which supplies the AVN/BH with blood, a specific change in thenavigation signal in the PR segment and QRS complex will be noticeable.Further specific changes of the navigation signal according to thepresent Invention will be observed as the catheter tip is advanced intothe coronaries, or into the descending aorta, or into the carotidarteries, or even into the pulmonary veins.

FIG. 3 illustrates a method of catheter tip navigation to the CAJ basedon navigation signals calculated according to the present Invention forupper body venous access. In one embodiment of the present Invention, aCE and an RE are placed according to FIG. 2 and a catheter is insertedin a brachial vein (208,224). In one embodiment of the presentinvention, one navigation parameter is calculated as the sum Σ_(M) ofthe relevant maximum amplitudes of the navigation signal for each heartcycle. Σ_(M) is calculated according to equation (830) in FIG. 8,whereby A_(M) is the maximum amplitude of the navigation signal alignedto the R-peak of the heart cycle, P_(M+) is the maximum positiveamplitude of the navigation signal aligned with the P-segment of theheart cycle, P_(M−) is the maximum negative amplitude of the navigationsignal aligned with the P-segment of the heart cycle, and T_(M) is themaximum amplitude of the navigation signal aligned with the T-wave ofthe heart cycle. A biphasic navigation signal aligned with the P-wave ofthe heart cycle will contribute with both values P_(M)+ and P_(M−) toΣ_(M). In one embodiment of the present Invention, the algorithmcalculates only one value A_(M) aligned with the R-peak of the heartcycle and only one value T_(M) aligned with the T-wave. A_(M) and T_(M)can be positive or negative.

Close to an access point in the brachial vein (208), the navigationsignal computed according to the present invention (250) has a maximumnegative amplitude of value A_(M1). According to illustration (250), thenavigation parameter Σ_(M1)=A_(M1). This value is displayed on the graph(300) in FIG. 3 at location (abscissa) 1 (305). When the catheter isadvanced into the subclavian vein (206), the maximum negative amplitudeof the navigation signal decreases to A_(M2) (252) and the navigationparameter Σ_(M2)=A_(M2). This value is displayed on graph (300) atlocation (abscissa) 2 (310). The catheter is further advanced towardsthe innominate vein (214) right below the CE (245) and it reaches alocation in the vasculature beneath the CE where the navigation signalis illustrated by (256). The maximum amplitude value (A_(M3)) alignedwith the R-peak of the heart cycle is computed. It can have a smallpositive value, a small negative value or be practically zero. The valueΣ_(M3)=A_(M3) is displayed in graph (300) at location (abscissa) 3(315).

In general, the maximum amplitude aligned with the R-peak when thecatheter tip is closest to the CE, is minimal or close to zero. A smallbiphasic signal can also be an indication that the catheter tip isclosest to the CE. If the catheter is further advanced in the superiorvena cava (204), the navigation signal will show small a positivemaximum amplitude aligned with the R-peak (260). The value of thenavigation parameter in this case Σ_(M4)=A_(M4) is displayed on graph300 at location (abscissa) 4 (320). When the catheter tip reaches theCAJ, the navigation signal illustrated in FIG. 262) has two maxima: onealigned with the R-peak (A_(M5)) and one aligned with the P-segment(P_(M5+)) of the heart cycle. Both maxima are in this case positive. Thevalue of the navigation parameter at this catheter tip locationΣ_(M5)=A_(M5)+P_(M5+) is displayed on graph 300 at location (abscissa) 5(325). When the catheter tip is advanced into the right atrium thesignal at the tip of the catheter calculated according to the presentInvention is illustrated in FIG. 2 (264). The navigation signal has asmall positive maximum (A_(M6)) aligned with the R-peak of the heartcycle and a negative (P_(M6−)) and a positive maximum (P_(M6+)) valuesaligned with the P segment of the heart cycle. The value of thenavigation parameter at this catheter tip location in the RA isΣ_(M6)=A_(M6)+P_(M6+)+P_(M6−) and is displayed on graph 300 at location(abscissa) 6 (330). When the catheter tip is advanced into the IVC thesignal at the tip of the catheter calculated according to the presentInvention is illustrated in FIG. 2 (268). The navigation signal has asmall negative maximum (A_(M9)) aligned with the R-peak of the heartcycle and a negative maximum (P_(M9−)) aligned with the P segment of theheart cycle. The value of the navigation parameter at this catheter tiplocation in the IVC is Σ_(M9)=A_(M9)+P_(M9−) and is displayed on graph300 at location (abscissa) 9 (333). When the catheter tip is advancedinto the RV, the signal at the tip of the catheter calculated accordingto the present Invention is illustrated in FIG. 2 (269). The navigationsignal has a positive maximum (A_(M10)) aligned with the R-peak of theheart cycle and a positive maximum (T_(M10)) aligned with the T segmentof the heart cycle. In one embodiment of the present Invention, thevalue of the navigation parameter at this catheter tip location in theRV is calculated as Σ_(M10)=A_(M10)+T_(M10) and is displayed on graph300 at location (abscissa) 10 (335). In another embodiment of thepresent Invention, the value of the navigation parameter at thiscatheter tip location in the RV is calculated as Σ_(M10a)=A_(M10a).

In a different situation, the catheter inserted in the brachial vein(208) can navigate into the subclavian vein (206), reach the innominatevein and then navigate into a jugular vein. When the catheter tip is ina jugular vein (212, 216), the navigation signal according to thepresent invention is illustrated by (254) and has a negative maximumvalue of A_(M7). The sequence of catheter tip locations in this case isillustrated by graph (340) in FIG. 3. The value Σ_(M1)=A_(M1) of thenavigation parameter obtained when the catheter is inserted in thebrachial vein is represented as (340), the value Σ_(M2)=A_(M2) in thesubclavian vein as (345), the value Σ_(M3)=A_(M1) at the point closestto the CE as (350), and, finally, the value Σ_(M7)=A_(M7) in the jugularvein at location (abscissa) 7 as (355).

In yet a different situation, the catheter inserted in the brachial vein(208) can navigate into the subclavian vein (206), reach the innominatevein and then navigate into the contralateral subclavian vein (220).When the catheter tip is in the contralateral subclavian vein, thenavigation signal according to the present invention is illustrated by(258) and has a negative maximum value of A_(M8). The sequence ofcatheter tip locations in this case is illustrated by graph (360) inFIG. 3. The value Σ_(M1)=A_(M1) when the catheter is inserted in thebrachial vein is represented as (365), the value in the subclavian veinΣ_(M2)=A_(M2) as (370), the value Σ_(M3)=A_(M3) at the point closest tothe CE as (375), and, finally, the value Σ_(M8)=A_(M8) in thecontralateral subclavian vein at location 8 as (380).

From these illustrations and embodiments it can be seen that thenavigation signal and the navigation parameter calculated according tothe present Invention can be used to navigate the catheter towards andplace the catheter tip at certain locations in the vasculature, inparticular in and around the heart. In order to achieve this goal, thepresent Invention introduces a new catheter navigation and positioningmethod, which in one embodiment consists of the following steps:

-   -   1. Place a reference electrode on the patient's left lower        abdomen, e.g. right below the lowest rib. Make an electrical        connection between the electrode and the apparatus according to        the present invention.    -   2. Place a control electrode on the patient's skin in a position        relevant to the target location for the catheter tip in the        vasculature, e.g., below the sternal notch over the manubrium of        the sternum. Make an electrical connection between the control        electrode and the apparatus according to the present invention.    -   3. Insert the catheter in the vasculature (artery or vein)        according to standard clinical procedures.    -   4. Make an electrical connection between the distal end of the        catheter (catheter tip), the proximal end of the catheter and        the apparatus according to standard clinical procedures.    -   5. Watch the navigation signal provided by the apparatus        according to the present Invention.    -   6. Watch the amplitude of the signal aligned with the R-peak of        the heart cycle and follow the map of the navigation signal        according to the present invention in order to estimate the        location of the catheter tip relative to the control electrode.    -   7. Watch the amplitude or amplitudes of the signal aligned with        the P segment of the heart cycle and follow the map of the        navigation signal according to the present invention in order to        estimate the location of the catheter tip relative to the CAJ.    -   8. Watch the amplitude of the signal aligned with the QRS        complex and the T segment of the heart cycle and follow the map        of the navigation signal according to the present invention in        order to estimate the location of the catheter tip relative to        the ventricles.    -   9. Watch the amplitude of the signal aligned with the QRS        complex and with the PR segment and follow the map of the        navigation signal according to the present invention in order to        estimate the location of the catheter tip relative to the        coronary arteries and the aortic arch.    -   10. Choose your desired catheter tip location based on the        navigation map according to the present Invention and place the        catheter tip at that location.    -   11. Finish the catheter placement procedures according to the        standard clinical procedures.

The herein presented embodiment of the catheter navigation andpositioning method is not a limitation of the current Invention. Otherembodiments and variations of this method are possible which are obviousto those skilled in the art.

FIG. 4 illustrates the apparatus connected to patient in supine positionfor cannulation of the femoral vein or femoral artery. A CE (420) ispositioned on the patient at a location of interest. In one embodimentof this Invention illustrated in FIG. 2, the CE is placed on thepatient's sternum over the xiphoid process. This skin position isestimated to be the closest position on the skin corresponding in thevasculature to the inferior vena cava (IVC) below the heart. Inaddition, this position is easily identifiable by anatomical landmarksand is independent of the side of the femoral vascular access location(left or right). For the same targeted position of the catheter tip inthe vasculature, the CE may be placed at other locations on the skin, aswell. The CE may be placed at other locations on the skin for differenttargeted positions of the catheter tip.

An RE (410) is placed on the patient's skin. In one embodiment of theInvention, the RE is placed on the left lower patient abdomen rightbelow the lowest rib. The RE may be placed at other locations, as well.A catheter (430) is inserted into the vasculature of the patient byfemoral access and electrical connectivity is ensured between the distalend of the catheter (432) and its proximal end (434). Such electricalconductivity can be ensured with currently available means, e.g., byusing a conductive wire between the catheter ends or by injectiveelectrically conductive solution like saline or heparin into thecatheter. The proximal end of the catheter (434) is electricallyconnected to the apparatus (440) according to the present Invention. TheCE (420) and the RE (410) are also electrically connected to theapparatus (440). The apparatus (440) measures an electrical signal (450)at the CE relative to the RE and another electrical signal (454) at thedistal end of the catheter relative to the RE.

The apparatus computes a navigation signal based on the signal (454)obtained from the distal end of the catheter and from the signal (450)obtained from the CE. The signal (454) at the catheter tip is, incertain locations in the vasculature, determined by the ECSH, forexample by a natural pacemaker of the heart (460) and the relativelocation of the catheter tip (462) to this pacemaker. The electricalsignals obtained from the CE and from the tip of the catheter may begenerated by the natural body pacemakers, e.g., the sino-atrial node orthe atrio-ventricular node, by artificial (implanted) pacemakers or byelectrical generators external to the body.

FIG. 5 illustrates a map of navigation signals according to the presentInvention for navigation to the CAJ, RA, IVC, and RV in the case offemoral or saphenous venous access. Besides the heart (500), thesuperior vena cava (502), and the left (504) and right (506) subclavianveins, FIG. 5 illustrates the following elements of the venous systemand of the ECSH: the CAJ (508), the RA (509), the SAN (510), the AVN/BH(511), the PF (513), in addition to the inferior vena cava (516), thehepatic veins (512), the renal veins (514), the femoral veins (518), theiliac veins (520), and the saphenous veins (522). The illustratedanatomical landmarks are: the xiphoid process (534), the right and leftlowest ribs (532), and the umbilicus (530).

If an CE (542) is placed on the patient's sternum over the xiphoidprocess (534) and an RE (540) is placed right below the lowest left ribon the patient's left abdomen then the illustrated navigations signalsare computed and displayed according to the present Invention. In afemoral or saphenous vein (518 or 522), the navigation signal willpresent large negative amplitude aligned with the R-peak of the heartcycle (560). In an iliac vein or in the inferior vena cava just aboutthe junction with the iliac veins, the navigation signal will presentsmaller negative amplitude aligned with the R-peak (562). Advancing thecatheter tip into the inferior vena cava (516) and approaching the CE(542) will result in a small biphasic navigation signal (564). Thebiphasic aspect of the navigation signal when the catheter tip isclosest to the CE is a result of a difference in phase between the ECGwaveforms at the tip of the catheter and at the CE. The closer the tipof the catheter is to the CE, the smaller the phase differenceillustrated by (564). This phase difference may be used according to thepresent Invention to determine when the catheter tip is closest to theCE and to analyze the trend of the catheter tip movements towards andaway from the CE. Further advancing the catheter tip into the rightatrium (509) will result in a navigation signal (566) with a smallpositive peak aligned with the R-peak of the heart cycle and with abiphasic signal aligned with the P segment of the hear cycle having onenegative and one positive maximum values (566). When the catheter tipreaches the CAJ (508), the navigation signal is illustrated by (570)with a maximum positive value aligned with the R-peak and one maximumpositive value aligned with the P segment of the heart cycle. If thecatheter is advanced into the SVC, the navigation signal (568) will showa small positive maximum value aligned with the R-peak of the heartcycle.

These illustrations are not limitations of the present Invention. Othershapes of the navigation signals can be calculated as indicative of thelocations in the vasculature. Such different shapes or variations of thenavigation signal may depend on the location of the CE and the RE, maybe a result of patient variability, of certain parameters of thecomputation algorithms, etc.

In another embodiment of the present Invention, a navigation map can bedeveloped according to the present invention for catheter locations inthe arterial system for the same placement of the CE and RE as in FIG.5. The arterial access in the arterial access situation is performed byfemoral cannulation. The catheter is then advanced into the abdominalaorta, into the descending aorta, into the aortic arch and then furtherinto the coronary arteries. As the catheter tip approaches the end ofthe abdominal aorta and the beginning of the descending aorta which isclosest to the CE, a biphasic navigation signal as the one illustratedin FIG. 5 (564) will be calculated according to the present Invention.As, for example, the catheter tip is advanced into the right coronaryartery, which supplies the AVN/BH with blood, a specific change in thenavigation signal in the PR segment and QRS complex will be noticeable.Further specific changes of the navigation signal according to thepresent Invention will be observed as the catheter tip is advanced intothe coronaries, or into the descending aorta, or into the carotidarteries, or even into the pulmonary veins.

FIG. 6 illustrates a method of navigation to the CAJ based on navigationsignals calculated according to the present Invention for saphenous orfemoral venous access. In one embodiment of the present invention anavigation parameter is calculated as the sum Σ_(M) of relevant maximumamplitudes of the navigation signal for each heart cycle. Σ_(M) iscalculated according to equation (830) in FIG. 8, whereby A_(M) is themaximum amplitude of the navigation signal aligned to the R-peak of theheart cycle, P_(M+) is the maximum positive amplitude of the navigationsignal aligned with the P-segment of the heart cycle, P_(M−) is themaximum negative amplitude of the navigation signal aligned with theP-segment of the heart cycle, and T_(M) is the maximum amplitude of thenavigation signal aligned with the T-wave of the heart cycle. A biphasicnavigation signal aligned with the P-wave will contribute with bothvalues P_(M+) and P_(M−) to Σ_(M). In one embodiment of the presentinvention, the algorithm calculates only one value A_(M) aligned withthe R-peak of the heart cycle and only one T_(M) value aligned with theT-wave of the heart cycle. A_(M) and T_(M) can be positive or negative.

Close to the femoral or saphenous access point, the navigation signalcomputed according to the present invention (560) has a maximum negativeamplitude of value A_(M1). According to illustration (560), thenavigation parameter at this catheter tip location is Σ_(M1)=A_(M1).This value is displayed on the graph (600) in FIG. 6 at location(abscissa) 1 (605). When the catheter is advanced into the IVC (516),the maximum negative amplitude of the navigation signal decreases toA_(M2) (562) and Σ_(M2)=A_(M2). This value is displayed on graph (600)at location (abscissa) 2 (610). The catheter is further advanced towardsthe CE and it reaches a location in the vasculature beneath the CE wherethe navigation signal is illustrated by (564). The maximum amplitudevalue (A_(M3)) aligned with the R-peak of the heart cycle is computedaccording to the present invention. The navigation signal can have asmall positive value, a small negative value or be practically zero. Thevalue Σ_(M3)=A_(M3) is displayed in graph (600) at location (abscissa) 3(615). In general, the maximum navigation signal amplitude aligned withthe R-peak when the catheter tip is closest to the CE, is minimal orclose to zero. A small biphasic signal can also be an indication thatthe catheter tip is closest to the CE. If the catheter is furtheradvanced in the RA (509), the signal at the tip of the cathetercalculated according to the present Invention is illustrated in FIG. 5(566).

The navigation signal has a small positive maximum (A_(M4)) aligned withthe R-peak of the heart cycle and a negative (P_(M4−)) and a positivemaximum (P_(M4+)) values aligned with the P segment of the heart cycle.The value of the navigation parameter at this catheter tip location inthe RA is Σ_(M4)=A_(M4)+P_(M4+)+P_(M4−) and is displayed on graph 600 atlocation (abscissa) 4 (620). When the catheter tip reaches the CAJ(508), the navigation signal illustrated in FIG. 5 (570) has two maxima:one aligned with the R-peak (A_(M5)) and one aligned with the P-segment(P_(M5+)) of the heart cycle. Both maxima are in this case positive. Thevalue of the navigation parameter at this catheter tip locationΣ_(M5)=A_(M5)+P_(M5+) is displayed on graph 600 at location (abscissa) 5(625). When the catheter tip is advanced into the SVC the signal at thetip of the catheter calculated according to the present Invention isillustrated in FIG. 5 (568). The navigation signal has a small positivemaximum (A_(M6)) aligned with the R-peak of the heart cycle. The valueof the navigation signal at this catheter tip location in the SVC isΣ_(M6)=A_(M6) and is displayed on graph 600 at location (abscissa) 6(630).

From these illustrations and embodiments it can be seen that thenavigation signal calculated according to the present Invention can beused to navigate the catheter towards and place the catheter tip atcertain locations in the vasculature, in particular in and around theheart. In order to achieve this goal, the present Invention introduces acatheter navigation and positioning method, which in one embodimentconsists of the following steps:

-   -   1. Place a reference electrode on the patient's left lower        abdomen, e.g. right below the lowest rib. Make an electrical        connection between the electrode and the apparatus according to        the present invention.    -   2. Place a control electrode on the patient's skin in a position        relevant to the target location for the catheter tip in the        vasculature, e.g., on the patient's sternum over the xiphoid        process. Make an electrical connection between the control        electrode and the apparatus according to the present invention.    -   3. Insert the catheter in the vasculature (artery or vein) by        femoral or saphenous access according to standard clinical        procedures.    -   4. Make an electrical connection between the distal end of the        catheter (catheter tip), the proximal end of the catheter and        the apparatus according to standard clinical procedures.    -   5. Watch the navigation signal provided by the apparatus        according to the present Invention.    -   6. Watch the amplitude of the signal aligned with the R-peak of        the heart cycle and follow the map of the navigation signal        according to the present invention in order to estimate the        location of the catheter tip relative to the control electrode.    -   7. Watch the amplitude or amplitudes of the signal aligned with        the P segment of the heart cycle and follow the map of the        navigation signal according to the present invention in order to        estimate the location of the catheter tip relative to the CAJ.    -   8. Watch the amplitude of the signal aligned with the QRS        complex and the T segment of the heart cycle and follow the map        of the navigation signal according to the present invention in        order to estimate the location of the catheter tip relative to        the ventricles.    -   9. Watch the amplitude of the signal aligned with the QRS        complex and with the PR segment and follow the map of the        navigation signal according to the present invention in order to        estimate the location of the catheter tip relative to the        coronary arteries and the aortic arch.    -   10. Choose your desired catheter tip location based on the        navigation map according to the present Invention and place the        catheter tip at that location.    -   11. Finish the catheter placement procedures according to the        standard clinical procedures.

The herein presented embodiment of the catheter navigation andpositioning method is not a limitation of the current Invention. Otherembodiments and variations of this method are possible which are obviousto those skilled in the art.

FIG. 7 illustrates the flow chart for generating navigation signals andparameters according to the present Invention. Electrical signals from aCE (701) and from an RE (700) are input to a measurement unit (704). Theelectrical signals from an RE (700) and from the tip of the catheterCATH (703) are input to another measurement unit (702). Any number ofsuch measurement units can be implemented for any number of CEs and anynumber of catheter sensors. The reference electrode can be the same forany number of such measurement units or there can be different referenceelectrodes for different measurement units. The signal generated by(704) is weighted with a coefficient CM (712) by the multiplication unit(708) and the signal generated by (702) is weighted with anothercoefficient CC (710) by the multiplication unit (706). CM and CC may beequal or different in value. The CM and CC values can be fixed oradaptive as a result of the analysis of the signals performed by thesignal analysis unit (790), which acts as an active feedback loop.

In one embodiment of the present Invention, the signal (714), whichoriginates at a CE is used by the peak detector unit TR (730) to detectthe timing of the R-peak of the QRS complex of each heart cycle. In oneembodiment of the present Invention, the TR unit (730) also calculatesthe duration of a heart cycle, i.e., the time interval between twoR-peaks. In one embodiment of the present Invention, the TR unit furthercalculates the heart rate. In one embodiment of the present Invention,the TR unit further calculates the number of data samples in a heartcycle using the duration of the heart cycle and the sampling rate forsampling/digitizing the navigation signal. The timing of the R-peak isused to synchronize and trigger different computations according to thepresent Invention. The timing of the R-peak can be also displayedtogether with the navigation signal and with navigation parameterscalculated according to the present Invention on the monitor (780).

In one embodiment of the present Invention, the unit (736) computes thestandard deviation S, of the navigation signal for each heart cycleaccording to equations (810) and (840) in FIG. 8. In one embodiment ofthe present Invention, the value of the standard deviation can be usedas a navigation parameter and can displayed on the monitor (780). In oneembodiment of the present Invention, the unit (732) computes theauto-correlation Cx of the navigation signal for each heart cycleaccording to (820), (810), and (840) in FIG. 8. In one embodiment of thepresent Invention, the value Cx of the auto-correlation is analyzed by athreshold detector (734) and used to filter out certain heart cyclesusing the switches (740) and (742). A high value of the auto-correlationCx may indicate a stable signal, while a low value of theauto-correlation Cx may indicate large variations between heart cyclesdue, for example, to noise. In one embodiment of the present Invention,if the auto-correlation value Cx is lower than a certain threshold, theheart cycle with that low auto-correlation value Cx is excluded fromfurther computations because it may not be relevant due to highvariability of the signal.

In one embodiment of the present Invention, the timing calculated by theTR unit (730) is used to trigger low-pass, band-pass, high-pass orselective filtering related to one or more heart cycles or to fractionsof the heart cycle by the filter units (722) and (720). Such filteringmay be different for the signals originating at a CE and at the cathetertip.

The unit (750) computes the difference signal between the signalsoriginating at a CE and at the catheter tip. In one embodiment of thepresent invention, a weighted average or weighted difference of the CEand catheter tip signal or signals is computed by the unit (750) inorder to generate a navigation signal. The weighted difference has theeffect of diminishing the elements of the ECG waveform which are similarbetween the CE and the catheter tip and thus enhancing the elements ofthe ECG waveform which are different. The similar elements are typicallythose static, i.e., not related to the catheter tip location. Thedifferent elements are typically those which change with the cathetertip location. For example, the R-peak of the ECG waveform is diminished,as is the T-wave if they do not change as a function of the catheter tiplocation. On the contrary, the P-wave changes are enhanced and so arechanges in the QRS complex or T-wave if these changes are related to thecatheter tip location. Thus the unit (750) enhances the ability todiscriminate between changes in the navigation signal which are relevantto catheter tip location changes.

In one embodiment of the present Invention, the difference signal isdisplayed on the monitor (780). In one embodiment of the presentInvention, the unit (752) computes the peak of the navigation signalA_(M), and uses the timing of the R-peak of the heart cycle to displayinformation about the synchronization between the navigation signal andthe heart cycle onto on the monitor (780).

In one embodiment of the present Invention, the unit (760) in FIG. 7detects baseline changes in the signal originating at the catheter tipand the unit (762) subtracts the baseline changes from the signal. Thebaseline removal function performed by units (760) and (762) isdifferent from standard filtering for baseline removal as known in theart. The baseline removal function performed by units (760) and (762)detects and removes such baseline variations which may occur due tocatheter navigation, i.e., due to the fact that the electrical signal atthe tip of the catheter is measured at different locations which may becharacterized by different levels of the baseline.

In one embodiment of the present Invention, the parameter computationunit (770) computes several quantitative navigation parameters from thenavigation signal:

-   -   a) The standard deviation of the ECG waveform during a heart        cycle and/or during a sequence of heart cycles and/or for a        certain time segment within a heart cycle, e.g., the P-segment        computed according to (810) in FIG. 8.    -   b) The sum of maximum relevant amplitudes of the navigation        signal for each heart cycle ΣM computed according to (830) in        FIG. 8.    -   c) The average value of the navigation signal for a heart cycle        and/or for a sequence of heart cycles and/or for a certain time        segment within a heart cycle, e.g., the P-segment computed        according to (840) in FIG. 8.    -   d) The relevant maximum amplitudes in a heart cycle: A_(M) (the        maximum amplitude of the navigation signal aligned with R-peak        of the heart cycle), P_(M−) (the maximum negative amplitude of        the navigation signal aligned with the P-segment of the heart        cycle), P_(M+) (the maximum positive amplitude of the navigation        signal aligned with the P-segment of the heart cycle), and TM        (the maximum amplitude of the navigation signal aligned with the        T-wave of the heart cycle).    -   e) The sum Σ_(i) of the sample values of the navigation signal        for a heart cycle and/or for a sequence of heart cycles and/or        for a certain time segment within a heart cycle, e.g., the        P-segment. The sum Σ_(i) is equivalent to the area (integral)        under the navigation signal in the navigation signal graph.

The herein illustrated quantitative parameters are not a limitation ofthe current Invention. Other parameters and variations of theseparameters are possible which are obvious to those skilled in the art.

In one embodiment of the present invention, these navigation parametersare displayed on the monitor (780). In one embodiment of the presentInvention, the navigation parameters computed by (770) are input to adirection evaluation unit (772) which analyzes these parameters in orderto detect a certain trend or direction in the catheter tip movements.For example, in one embodiment of the present Invention, the directionevaluation unit (772) determines if the catheter tip is moving towardsor away from a CE by analyzing the succession of relevant maximumamplitudes aligned with the R-peak of the heart cycle and by determiningwhen the navigation signal is biphasic and minimal in a certainsuccession. In another embodiment of the present Invention, thedirection evaluation unit (772) determines if the catheter tip is movingtowards or away from the CAJ by analyzing the succession of the valuesof the navigation parameter M.

In one embodiment of the present Invention, one parameter used fornavigation is the auto-correlation calculated according to (820) in FIG.8. In one embodiment of the present Invention, one parameter used fornavigation is the sum of maximum relevant amplitudes of the navigationsignal for each heart cycle M. The sum Σ_(M) is calculated according toequation (830) in FIG. 8, whereby A_(M) is the maximum amplitude of thenavigation signal aligned to the R-peak of the heart cycle, P_(M+) isthe maximum positive amplitude of the navigation signal aligned with theP-segment of the heart cycle, P_(M−) is the maximum negative amplitudeof the navigation signal aligned with the P-segment of the heart cycle,and T_(M) is the maximum amplitude of the navigation signal aligned tothe T-wave of the heart cycle. A biphasic P-wave will contribute withboth values P_(M+) and P_(M−) to Σ_(M). There exists only one valueA_(M) aligned with the R-peak of the heart cycle. A_(M) and TM can bepositive or negative. In one embodiment of the present Invention, oneparameter used for navigation is the sum of all signal samples Σ_(i) fora given time period of time. In one embodiment of the present invention,the average value of the navigation signal over a certain period of timeis computed according to (840) in FIG. 8.

In one embodiment of the present Invention, relevant positive andnegative amplitudes and their timing relative to the R-peak of the heartcycle are computed for each heart cycle from the navigation signal,e.g., A_(M) is the maximum amplitude of the navigation signal aligned tothe R-peak of the heart cycle, P_(M+) is the maximum positive amplitudeof the navigation signal aligned with the P-segment of the heart cycle,P_(M−) is the maximum negative amplitude of the navigation signalaligned with the P-segment of the heart cycle, and T_(M) is the maximumamplitude of the navigation signal aligned to the T-wave of the heartcycle. Each and all of these parameters can be computed according to thepresent Invention, for one heart cycle, and/or for several heart cycles,and/or or for a fraction of a heart cycle, e.g., for the P segment (thetime period corresponding to the P-wave).

The illustration in FIG. 7 is not a limitation of the current invention.Someone skilled in the art will find it obvious that other solutions arepossible to obtain the same results. Moreover, for someone skilled inthe art it will be obvious that elements and units illustrated in FIG. 7can be practically implemented in hardware and/or firmware and/orsoftware with alternative but equivalent solutions.

FIG. 8 illustrates parameter computation methods according to thepresent Invention. In one embodiment of the present Invention, thestandard deviation of the navigation signal Sx_(j) is computed accordingto (810), whereby n represents the number n of data samples xi for thej-th heart cycle, i=1,n. The value −x represents the average value ofthe data samples over the j-th heart cycle (840). The standard deviationcomputed according to (810) is a measure of the variations of thenavigation signal values around its average value during a heart cycle.For example, when the catheter tip is further away from the C_(E), thenthe value of the standard deviation Sx_(j) is larger than the value ofthe standard deviation Sx_(k) when the catheter tip is closest to theC_(E). Thus, the value of the standard deviation calculated according tothe present Invention can be used as a measure of the proximity of thecatheter tip to the C_(E).

In one embodiment of the present Invention, the auto-correlationcoefficient Cx_(j,j-1) is computed according to (820) for the navigationsignal x at the j-th heart cycle and at the previous j−1−the heartcycle, whereby n represents the number of data samples xi for the j-thheart cycle, i=1,n. The value ⁻x_(j) represents the average value of thedata samples over the j-th heart cycle computed according to (840). Thevalue ⁻x_(j-1) represents the average value of the data samples over thej−1-th heart cycle, i.e., of the one heart cycle before the j-th heartcycle. Sx_(j) is the standard deviation of the navigation signalcomputed according to (810) for the j-th heart cycle. Sx_(j-1) is thestandard deviation of the navigation signal computed according to (810)for the j-th heart cycle. In general, the number of samples n for thej-th heart cycle is different than the number of samples for the j-thheart cycle. According to the present Invention, n samples areconsidered for the calculation of both Sx_(j) and Sx_(j-1), whereby n isthe number of samples of the j-th heart cycle. The n samples for thecalculation of Sx_(j-1) are selected starting from the end of the j−1-thheart cycle as determined by the TR unit (730) in FIG. 7. In anotherembodiment of the Invention, the auto-correlation coefficient can becalculated using (820) as Cx_(j,k), whereby j and k are any two heartcycles. This includes the situation in which j=k and the coefficient iscalculated for the same heart cycle.

In one embodiment of the present Invention, one parameter used fornavigation is the sum of maximum amplitudes of the navigation signal foreach heart cycle M. In one embodiment of the present Invention, the sumΣ_(M) is calculated according to equation (830) in FIG. 8, whereby A_(M)is the maximum amplitude of the navigation signal aligned to the R-peakof the heart cycle, P_(M+) is the maximum positive amplitude of thenavigation signal aligned with the P-segment of the heart cycle, P_(M−)is the maximum negative amplitude of the navigation signal aligned withthe P-segment of the heart cycle, and T_(M) is the maximum amplitude ofthe navigation signal aligned to the T-wave of the heart cycle. Abiphasic navigation signal aligned with the P-segment of the heart cyclewill contribute with both values P_(M+) and P_(M−) to Σ_(M). In oneembodiment of the present Invention, the algorithm computes only onevalue A_(M) aligned with the R-peak of the heart cycle and only oneT_(M) value aligned with the T-wave of the heart cycle. A_(M) and T_(M)can be positive or negative. In another embodiment of the presentInvention, the sum Σ_(M) is calculated as:Σ_(M) =A _(M) +P _(M+) +P _(M−).

In one embodiment of the present Invention, the navigation parameters inFIG. 8, i.e., the standard deviation (810), the auto-correlation (820),the sum of relevant amplitudes (830), and the average value (840) arecomputed for a heart cycle. In another embodiment of the presentInvention, the navigation parameters in FIG. 8 are computed for severalconsecutive heart cycles. In another embodiment of the presentInvention, the navigation parameters in FIG. 8 are computed for afraction of a heart cycle, e.g., only for an interval/segment ofinterest within a heart cycle, e.g., for the P segment.

What is claimed is:
 1. An intravascular catheter navigation device,comprising: a computer comprising a monitor and a plurality ofmeasurement and computing units; a control electrode electricallyconnected to the computer, the control electrode designed for placementon a sternum of a patient over a xiphoid process; a catheter including atip electrically connected to the computer, wherein the computer isconfigured to: calculate a navigation signal from electrical signalsobtained from the control electrode and the tip of the catheter; andoutput to the monitor a plurality of positions of the tip of thecatheter with respect to the control electrode, wherein the outputincludes an amplitude of the navigation signal aligned with an R-wave ofan electrocardiogram (ECG) signal obtained from the control electrode,and wherein the plurality of positions enables a user to navigate thetip of the catheter to an internal target location.
 2. The intravascularcatheter navigation device according to claim 1, further comprising areference electrode electrically connected to the computer, thereference electrode designed for placement on a lower abdomen of thepatient.
 3. The intravascular catheter navigation device according toclaim 1, wherein the navigation signal is calculated as a weightedaverage of the electrical signals obtained from the control electrodeand the tip of the catheter.
 4. The intravascular catheter navigationdevice according to claim 1, wherein the navigation signal is calculatedas a weighted difference of the electrical signals obtained from thecontrol electrode and the tip of the catheter.
 5. The intravascularcatheter navigation device according to claim 1, wherein an enhancednavigation signal is calculated using cross-correlation over severalsuccessive periods of the navigation signal.
 6. The intravascularcatheter navigation device according to claim 1, wherein the output ofthe plurality of positions of the tip of the catheter with respect tothe control electrode includes the amplitude of the navigation signalaligned with a P-wave of the ECG signal obtained from the controlelectrode.
 7. The intravascular catheter navigation device according toclaim 6, wherein the output of the plurality of positions of the tip ofthe catheter with respect to the control electrode includes a weightedaverage of the amplitudes of the navigation signal aligned with theP-wave, the R-wave, and a T-wave of the ECG signal obtained from thecontrol electrode.
 8. The intravascular catheter navigation deviceaccording to claim 6, wherein the output of the plurality of positionsof the tip of the catheter with respect to the control electrodeincludes a weighted difference of the amplitudes of the navigationsignal aligned with the P-wave, the R-wave, and a T-wave of the ECGsignal obtained from the control electrode.
 9. The intravascularcatheter navigation device according to claim 1, wherein the tip of thecatheter is electrically connected to the computer via a conductivesolution positioned in a lumen of the catheter.
 10. The intravascularcatheter navigation device according to claim 1, wherein the tip of thecatheter is electrically connected to the computer via a conductivewire.